Common carp (Cyprinus carpio) insulin-like growth factor binding protein-2 (IGFBP-2): molecular cloning, expression profiles, and hormonal regulation in hepatocytes

Insulin-like growth factor binding protein-3 (igfbp-3) and igfbp-5 in yellowtail kingfish (Seriola lalandi): molecular characterization and expression levels under different nutritional status and stocking density

Insulin-like growth factor-binding proteins (IGFBPs) play important roles in regulating growth and development by binding to IGF, where IGFBP-3 and IGFBP-5 are the main binding carriers of IGF in the circulation system. In the present study, the gene sequences of igfbp-3, igfbp-5a, and igfbp-5b were cloned from the liver of yellowtail kingfish (Seriola lalandi). The ORF sequences of igfbp-3, igfbp-5a, and igfbp-5b were 888, 801, and 804 bp in length, which encoded 295, 266, and 267 amino acids, respectively. The above three genes were widely expressed in yellowtail kingfish tissues, with igfbp-3 being the most highly expressed in the heart, brain, and gonads, while igfbp-5a and igfbp-5b were both most highly expressed in the liver and kidney. The expression levels of igfbp-3, igfbp-5a, and igfbp-5b were detected throughout the embryonic and larval stages, suggesting their roles in early development and growth regulation of yellowtail kingfish. Besides, igfbp-3 and igfbp-5a were significantly up-regulated in the liver under food deprivation and high-density rearing conditions, which was exactly opposite to the growth performance of yellowtail kingfish, implying that they may serve as biomarkers of adverse culture conditions. Overall, the above results initially identified the molecular characteristics of igfbp-3/-5a/-5b in yellowtail kingfish and implied that they might play important roles in the growth and development, providing a basis for further research on underlying regulatory mechanisms.

Gene expression analyses of GH/IGF axis in triploid crucian carp with growth heterosis

Hybridization and polyploid breeding are the main approaches used to obtain new aquaculture varieties. Allotriploid crucian carp (3n) with rapid growth performance was generated by mating red crucian carp (RCC) with allotetraploids (4n). Fish growth is controlled by the growth hormone (GH)/insulin-like growth factor (IGF) axis. In the present study, we examined the expression characteristics of GH/IGF axis genes in hybrids F1, 4n, 3n, RCC and common carp (CC). The results showed that GHRa, GHRb, IGF1, IGF2, and IGF-1Ra were highly expressed in 3n compared with RCC and CC, whereas IGF3 was undetectable in the liver in RCC, CC and 3n. GHRa and GHRb had low expression in the 4n group. In hybrid F1, GHRa expression was low, whereas GHRb was highly expressed compared to the levels in RCC and CC. Moreover, in hybrid F1, the expression of IGF3 was higher, and the expression of IGF1 and IGF2 was lower than that in the RCC and CC, whereas the expression of IGF-1Ra was similar to that in RCC and CC. For the IGFBP genes, IGFBP1 had higher expression in 3n compared than that in RCC and CC, while other IGFBP genes were not high expressed in 3n. Among the genes detected in this study, 11 genes were nonadditively expressed in 3n, with 5 genes in the transgressive upregulation model. We proposed that the 11 nonadditive expression of GH/IGF axis genes is related to growth heterosis in 3n. This evidence provides new insights into hybridization and polyploid breeding from the perspective of hormone regulation.

Transcriptome analysis of the muscle of fast- and slow-growing phoenix barb (Spinibarbus denticulatus denticulatus)

Growth rate is a commercial trait in aquaculture that is influenced by multiple factors, among which genetic composition plays a fundamental role in the growth rate of species. The phoenix barb (Spinibarbus denticulatus denticulatus) is a widely distributed freshwater fish species in South China. Although S. d. denticulatus is reared in South China, the molecular mechanisms underlying the growth rate of the species remain unclear. Here, the authors performed transcriptome analysis of muscle tissues from fast-growing (FG) and slow-growing (SG) S. d. denticulatus at 90, 150, and 300 days after hatch (DAH) to elucidate its growth mechanism. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that differentially expressed genes (DEGs) between the two groups were enriched in pathways related to muscle growth, glycolysis, and energy and lipid metabolism. Nonetheless, a higher number of DEGs were identified in the FG vs. SG groups at 90 and 300 DAH compared with 150 DAH. DEGs identified at 90 DAH were mainly enriched in the GH/IGF axis, PI3K-Akt signalling pathway, AMPK signalling pathway and lipid metabolism highly expressed in FG individuals. DEGs identified at 300 DAH were mainly enriched in PI3K-Akt signalling pathway, glycolysis/gluconeogenesis, gene translation and lipid metabolism. In addition, some genes were expressed during the early growth stage in FG individuals but expressed during the late stage in SG individuals, indicating considerable variations in the expression profiles of growth-related genes at different developmental stages. Overall, these findings contribute to the understanding of the growth mechanism of S. d. denticulatus, which would be useful for the propagation of fast-growing breeds.

Molecular identification of grass carp igfbp2 and the effect of glucose, insulin, and glucagon on igfbp2 mRNA expression

The GH (growth hormone)/IGFs (insulin-like growth factors) system has an important function in the regulation of growth. In this system, IGFBPs play a crucial regulatory role in IGF functions. As a member of the IGFBP family, IGFBP2 can bind to IGF and regulate IGF functions to regulate development and growth. In addition, IGFBP2 shows key regulatory functions in cell proliferation and metabolism. In this study, the igfbp2 gene was cloned from grass carp (Ctenopharyngodon idellus) liver. The ORF of grass carp igfbp2 is 834 bp long and encodes 277 amino acids. The tissue distribution results showed that igfbp2 is expressed in multiple tissues in grass carp and has a high expression level in the liver. In the OGTT, igfbp2 expression was significantly decreased in the liver and brain after 6 h of treatment with glucose. In vitro, igfbp2 expression in grass carp's primary hepatocytes was significantly suppressed by insulin after treatment for 6 and 12 h. Moreover, igfbp2 expression was markedly increased in a dose-dependent manner with glucagon incubation in grass carp's primary hepatocytes. To the best of our knowledge, this is the first report about Igfbp2 in grass carp. These results will provide a basis for the in-depth study of grass carp Igfbp2.

Molecular cloning and expression pattern of IGFBP-2a in black porgy (Acanthopagrus schlegelii) and evolutionary analysis of IGFBP-2s in the species of Perciformes

Insulin-like growth factor-binding protein-2 (IGFBP-2) plays a key role in regulating growth and development by its affinity with insulin-like growth factors (IGFs). In this study, we cloned the coding sequence (CDS) of IGFBP-2a from the black porgy (Acanthopagrus schlegelii) muscle and identified that the full-length CDS of IGFBP-2a was 882 bp. Real-time quantitative PCR revealed that IGFBP-2a was most abundant in the liver of the black porgy and backcross breed (F1♀×black porgy♂) but remained lower in each tested tissue in self-cross breed (F1♀×F1♂). In addition, the IGFBP-2a expression in the liver of three breeds showed a negative correlation with their growth rates, indicating that the IGFBP-2a played a growth-inhibiting role in the three breeds. We further identified 810 bp IGFBP-2b gene from the draft genome of black porgy. Finally, we examined the IGFBP-2a and IGFBP-2b genes by scanning the genomes of the species of Perciformes and found the IGFBP-2 gene duplication took place earlier than the divergence of perciform species. Interestingly, six positively selected sites were detected in both Perciformes IGFBP-2 genes, although both genes were identified to be under purifying selection. Specially, these positively selected sites were located in the functional domains, suggesting these sites played key roles in the growth of Perciformes. Our study partially explains the molecular basis for the prepotency in black porgy hybrids, which will provide guidance for their cultivation in the future.

Molecular cloning and expression profiles of IGFBP-1a in common carp (Cyprinus carpio) and its expression regulation by growth hormone in hepatocytes

In this study, we cloned and determined IGFBP-1a cDNA from common carp (Cyprinus carpio) liver. The 1655 bp full-length cDNA consisted of a 96 bp 5-untranslated region (UTR), a 789 bp open reading frame encoding 262 amino acid residues and a 770 bp 3-UTR containing seven mRNA instability motifs. Northern blot revealed a 1.8 kb IGFBP-1a transcript. IGFBP-1a mRNA was widely distributed in all tissues examined and predominantly expressed in the liver. During embryogenesis, IGFBP-1a mRNA was firstly observed in blastula stage, and significant increases were observed in body segment stage, lens formation stage and blood cycling stage. After hatching, its expression increased more than twenty times. Furthermore, hypoxia could significantly up-regulate IGFBP-1a expression in the liver and brain. IGFBP-1a expression increased with ovarian maturation and decreased at regressed stage. In testis, IGFBP-1a mRNA maintained relatively higher levels at recrudescing and matured stages, while it sharply declined at regressed stage. In primary cultured hepatocytes, IGFBP-1a gene was greatly down-regulated by growth hormone via the MAPK and PI3 kinase signaling pathways. These results suggest that IGFBP-1a may be involved in the IGF system regulating growth, development and reproduction in common carp.

Insulin-Like Growth Factor-Binding Proteins of Teleost Fishes

The insulin-like growth factor (Igf) binding protein (Igfbp) family has a broad range of physiological functions and a fascinating evolutionary history. This review focuses on the Igfbps of teleost fishes, where genome duplication events have diversified gene repertoire, function, and physiological regulation-with six core Igfbps expanded into a family of over twenty genes in some lineages. In addition to briefly summarizing the current state of knowledge on teleost Igfbp evolution, function, and expression-level regulation, we highlight gaps in our understanding and promising areas for future work.

Molecular identification of an insulin growth factor binding protein (IGFBP) and its potential role in an insulin-like peptide system of the pearl oyster, Pinctada fucata

Insulin-like growth factors (IGFs) play critical roles in regulating metabolism, growth, and reproduction in invertebrates. IGF binding proteins (IGFBPs) serve as major regulators of IGF activity and regulate endocrine system. In the present study, the full-length cDNA of an igfbp was identified from the pearl oyster, Pinctada fucata, using expressed sequence tag (EST) sequence. The 1124bp Pfigfbp cDNA contains a 465bp open reading frame (ORF) encoding a putative protein of 154 amino acids, a 5'-untranslated region (UTR) of 238bp, and a 3'-UTR of 394bp (not including polyA+). Multiple sequence alignment of the deduced IB domain sequences revealed that twelve conserved Cys and ILP binding site in PfIGFBP were well aligned with human IGFBPs1-7, Mizuhopecten yessoensis IGFBP5 and Eriocheir sinensis IGFBP7. Gene expression analysis indicated that Pfigfbp mRNA was expressed in all the tissues and developmental stages examined, with a higher level in the foot than in other tissues and a higher level in the polar body stage and 32-cell stage than in the other stages. Pfigfbp and PfILP (insulin-like peptide) mRNA levels significantly increased in the digestive gland after feeding, while levels were dramatically reduced during a week of food deprivation and increased upon refeeding. In vitro experiments indicated that Pfigfbp mRNA expression in mantle cells was affected by insulin/IGFs (IGF-I, IGF-II). Our data suggests that Pfigfbp may be involved in endocrine signaling in P. fucata via the regulation of insulin-like peptide signaling.

Cloning, molecular characterization and expression analysis of insulin-like growth factor binding protein-2 (IGFBP-2) cDNA in goldfish, Carassius auratus

In the present study, a full-length cDNA encoding the insulin-like growth factor binding protein-2 (IGFBP-2) was cloned from the liver of goldfish (Carassius auratus) by rapid amplification of cDNA ends technique. The goldfish IGFBP-2 cDNA sequence was 1,513 bp long and had an open reading frame of 825 bp encoding a predicted polypeptide of 274 amino acid residues. Semi-quantitative RT-PCR results revealed that goldfish IGFBP-2 mRNA was expressed in all detected tissues. In liver, central nervous system and pituitary gland, goldfish IGFBP-2 expressed at high levels, followed by anterior intestine, middle intestine and kidney. In posterior intestine, ovary, skin, fat, spleen, muscle and gill, the goldfish IGFBP-2 expression levels were very low. Fasting and refeeding experiment showed that the mRNA expression of goldfish IGFBP-2 was up-regulated significantly in liver compared to the fed group and restored rapidly to normal level after refed. However, the mRNA expressions of IGFBP-2 in hypothalamus and pituitary of goldfish were insensitive to fasting. Furthermore, the mRNA expressions of IGFBP-2 in hypothalamus, pituitary and liver were varied in periprandial changes and significantly down-regulated at 2 and 4 h after meal. These results imply that the IGFBP-2 mRNA expression may be associated with anabolic and catabolic metabolism and regulated by metabolic factors in goldfish.

Gonadal transcriptomic analysis of yellow catfish (Pelteobagrus fulvidraco): identification of sex-related genes and genetic markers

Yellow catfish (Pelteobagrus fulvidraco) has been recognized as a vital freshwater aquaculture species in East and Southeast Asia. In addition to its commercial interest, it is also attracted much attention because of its value in studying sex-determination mechanisms. A comprehensive gonadal transcriptome analysis is believed to provide a resource for genome annotation, candidate gene identification, and molecular marker development. Herein, we performed a de novo assembly of yellow catfish gonad transcriptome by high-throughput Illumina sequencing. A total of 82,123 contigs were obtained, ranging from 351 to 21,268 bp, and N50 of 2,329 bp. Unigenes of 21,869 in total were identified. Of these, 229 and 1,188 genes were found to be specifically expressed in XY gonad tissue for 1 yr and 2 yr old yellow catfish, respectively; correspondingly, 51 and 40 genes were identified in XX gonad tissue at those two stages. Gene ontology and KEGG analysis were conducted and classified all contigs into different categories. A large number of unigenes involved in sex determination were identified, as well as microsatellites and SNP variants. The expression patterns of sex-related genes were then validated by quantitative real-time PCR (qRT-PCR) suggesting the high reliability of RNA-Seq results. In this study, the transcriptome of yellow catfish gonad was first sequenced, assembled, and characterized; it provides a valuable genomic resource for better understanding of yellow catfish sex determination as well as development of molecular markers, thereby assisting in the production of monosex yellow catfish for aquaculture.

Molecular cloning, expression profiles and promoter analysis of insulin-like growth factor binding protein-4 (IGFBP-4) in Japanese flounder (Paralichthys olivaceus)

We cloned and characterized cDNA sequence of insulin-like growth factor binding protein-4 (IGFBP-4) from Japanese flounder (Paralichthys olivaceus). The 1493 bp full-length cDNA sequence contained an open reading frame (ORF) of 780 bp, which encoded a protein of 259 amino acids. The deduced amino acid sequences included a putative signal peptide of 28 amino acid residues resulting in a mature protein of 231 amino acids. Twenty cysteine residues and two conserved IGFBPs motif (GCGCCXXC and CWCV) were found in the N- and C-terminal domain. In the over 13 kbp genomic sequence, four exons, three introns, and 5'-/3'-flanking sequences were identified. Sequence alignment and phylogenetic analysis showed that Japanese flounder IGFBP-4 was indeed the ortholog of the human IGFBP-4 gene and shared high identities with other teleost IGFBP-4 genes. The promoter region was also analyzed and several potential transcription factor (TF) binding sites were determined which may modulate the IGFBP-4 expression. Quantitative real-time PCR analysis revealed that IGFBP-4 mRNA was observed in various tissues, with intestine showing the highest expression. The maternal transcripts of IGFBP-4 gene existed in the early embryonic stages and then increased in the following stages until hatching, suggesting that IGFBP-4 may be involved in the fish early development. The expression level of IGFBP-4 mRNA was relatively higher at 3 days post hatching (dph) and 15 dph, and gradually decreased during the metamorphosis period. All these results indicated that IGFBP-4 plays a significant role in IGF regulating vertebrate growth and development.

Insulin-like growth factor binding protein-2 (IGFBP-2) in Japanese flounder, Paralichthys olivaceus: molecular cloning, expression patterns and hormonal regulation during metamorphosis

In this study, we cloned and characterized cDNA sequences of two insulin-like growth factor binding protein-2 (IGFBP-2a and IGFBP-2b) from Japanese flounder, Paralichthys olivaceus. The full-length cDNA of IGFBP-2a is 1,046 bp long and consists an open frame (ORF) of 876 bp, a 5'-untranslated region (UTR) of 125 bp and a 3'-UTR of 45 bp. IGFBP-2b is 1,067 bp, including a 5'-UTR of 53 bp, a 3'-UTR of 198 bp and an ORF of 816 bp. Real-time quantitative PCR results revealed that IGFBP-2a -2b mRNA was expressed in all detected tissues. Interestingly, the levels of IGFBP-2a mRNA in all detected tissues were higher in female than male, but IGFBP-2b was precisely the opposite. At different embryonic stages, the levels of IGFBP-2a mRNA were typically higher than IGFBP-2b. After hatching, IGFBP-2a mRNA was gradually decreased to a relatively lower level. However, the expression of IGFBP-2b mRNA was increased after hatching, including 3, 7, 10, 14, 17, 20 and 23 days post-hatching (dph), and it presents a higher level until 29 (metamorphic climax), 36 (post-climax) and 41 dph (the end of metamorphosis). In levothyroxine sodium salt (T4, the main form of thyroid hormone in animals)-treated and thiourea (TU)-treated larvae, the expressions of IGFBP-2a had not visibly changed, except in T4-treated 17 dph larvae. The expressions of IGFBP-2b mRNA were distinctly increased from 17 to 23 dph, but suddenly dropped to a lower level in and after 29 dph. However, the levels of IGFBP-2b mRNA during metamorphosis were greatly down-regulated after TU treatment. These results provided basic information for further studies on the role of IGF system in flatfish development and metamorphosis.

Insulin-like growth factor binding protein 7, a member of insulin-like growth factor signal pathway, involved in immune response of small abalone Haliotis diversicolor

Insulin-like growth factor binding protein 7 (IGFBP7), the only member of the IGFBP superfamily that binds strongly to insulin, may have different functions from other IGFBPs. Unlike other IGFBPs, there is no knowledge available on aquatic invertebrate IGFBP7. In this study, a molluscan IGFBP7 gene, saIGFBP7, was cloned for the first time from the small abalone Haliotis diversicolor. Its full-length cDNA sequence is 1812 bp, with a 720 bp open reading frame encoding a protein of 239 aa. The molecular mass of the deduced protein is approximately 25.37 kDa with an estimated pI of 5.00, and it shares highest 41% identity to IGFBP7 of Amblyomma americanum. Analysis of conserved domains revealed the presence of an IGFBP N-terminal domain (IB), a kazal-type serine proteinase inhibitor domain (KI), and an immunoglobulin-like C2 domain (IgC2) in saIGFBP7. Furthermore, the 12 cysteine residues and the signature amino acid motif 'xCGCCxxC' which are characterized by the amino terminus region of the IGFBP superfamily are all presented in saIGFBP7. Quantitative real-time PCR and western blot were employed to investigate the tissue distribution of saIGFBP7, and its expression under bacterial challenge. The saIGFBP7 mRNA and protein could be detected in all examined tissues, with the highest expression level in hemocytes, higher expression level in gills, and was up-regulated in hemocytes and gills after bacterial injection. In addition, saIGFBP7 mRNA transcripts were observed in a subset of the branchial epithelium and the nucleus of hemocytes using the in situ hybridization method. Interestingly, saIGFBP7 was detected mainly in the goblet-like cell of the branchial epithelium by immunohistochemistry. These results suggested that saIGFBP7 was likely to be involved in a function associated with pathogenic infection and may play an important role in the adult abalone immune system.

Identification and expression analysis of IGFBP-1 gene from Japanese flounder (Paralichthys olivaceus)

Insulin-like growth factor binding protein-1 (IGFBP-1) plays an important role in IGF regulating vertebrate growth and development. In this study, we cloned IGFBP-1 cDNA from Japanese flounder (Paralichthys olivaceus) liver. The full-length cDNA is 1070 bp, including a 5'-untranslated region (UTR) of 69 bp, a 3'-UTR of 272 bp, and an open reading frame (ORF) of 729 bp encoding a polypeptide of 242 amino acids. Real-time quantitative PCR revealed that IGFBP-1 mRNA is mainly expressed in the liver, and a small amount of mRNAs was also found in other adult tissues. There are maternal transcripts of IGFBP-1 gene, and relatively low mRNA levels were observed in different embryonic stages. A higher level of IGFBP-1 mRNA was detected at 3 days post hatching (dph), and it got to the highest level at 29 dph (metamorphic climax), and finally brought back to a lower level at the end of metamorphosis. The expression of IGFBP-1 mRNA was greatly up-regulated in thyroid hormone (TH)-treated larvae, and declined after thiourea (TU) treatment. These results provide basic information for further studies on the role of IGF system in the P. olivaceus development and metamorphosis.

Characterization of three IGFBP mRNAs in Atlantic croaker and their regulation during hypoxic stress: potential mechanisms of their upregulation by hypoxia

Insulin-like growth factor-binding proteins (IGFBPs) play important roles in downregulating IGF activity and growth and development in vertebrates under hypoxic stress. However, the mechanisms of hypoxia regulation of IGFBPs in teleost fishes are unknown. The involvement of reactive oxygen species (ROS) and hypoxia-inducible factors (HIFs) in hypoxia upregulation of IGFBPs in Atlantic croaker were investigated. Three croaker IGFBPs, IGFBP-1, IGFBP-2, and IGFBP-5, were cloned and characterized. Chronic hypoxia exposure [dissolved oxygen (DO): 1.7 mg/l for 2-4 wk] caused significant increases in hepatic and neural IGFBP-1 mRNA expression compared with tissue mRNA levels in fish held under normoxic conditions (6.5 mg DO/l). Moreover, longer-term chronic hypoxia exposure (2-2.7 mg DO/l for 15-20 wk) caused significant increases in mRNA levels of all three IGFBPs in both liver and brain tissues. Hypoxia exposure also markedly increased superoxide radical (O(2)(·-), an index of ROS) production and HIF-1α mRNA and HIF-2α protein expression in croaker livers. Pharmacological treatment with an antioxidant attenuated the hypoxia-induced increases in O(2)(·-) production and HIFα mRNA and protein expression as well as the elevation of IGFBP-1 mRNA levels. These results suggest that the upregulation of IGFBP expression under hypoxia stress is due, in part, to alterations in the antioxidant status, which may involve ROS and HIFs.

Evolution of the insulin-like growth factor binding protein (IGFBP) family

The evolution of the IGF binding protein (IGFBP) gene family has been difficult to resolve. Both chromosomal and serial duplications have been suggested as mechanisms for the expansion of this gene family. We have identified and annotated IGFBP sequences from a wide selection of vertebrate species as well as Branchiostoma floridae and Ciona intestinalis. By combining detailed sequence analysis with sequence-based phylogenies and chromosome information, we arrive at the following scenario: the ancestral chordate IGFBP gene underwent a local gene duplication, resulting in a gene pair adjacent to a HOX cluster. Subsequently, the gene family expanded in the two basal vertebrate tetraploidization (2R) resulting in the six IGFBP types that are presently found in placental mammals. The teleost fish ancestor underwent a third tetraploidization (3R) that further expanded the IGFBP repertoire. The five sequenced teleost fish genomes retain 9-11 of IGFBP genes. This scenario is supported by the phylogenies of three adjacent gene families in the HOX gene regions, namely the epidermal growth factor receptors (EGFR) and the Ikaros and distal-less (DLX) transcription factors. Our sequence comparisons show that several important structural components in the IGFBPs are ancestral vertebrate features that have been maintained in all orthologs, for instance the integrin interaction motif Arg-Gly-Asp in IGFBP-2. In contrast, the Arg-Gly-Asp motif in IGFBP-1 has arisen independently in mammals. The large degree of retention of IGFBP genes after the ancient expansion of the gene family strongly suggests that each gene evolved distinct and important functions early in vertebrate evolution.